Linear compressor with permanent magnets

ABSTRACT

This invention provides a compressor with brushless single-phase linear motor, which includes a movable cylinder associated with a permanent magnet array, at least a stationary electromagnetic winding set and a pair of stationary pistons. A partition plate is disposed in the movable cylinder to form a first sub-cylinder and a second sub-cylinder. The front ends of the pair of the stationary pistons are respectively placed in either of two openings of the movable cylinder at its two ends. An alternate current applied to the stationary electromagnetic winding set to generate alternately attracting/repelling forces to the permanent magnet array. The movable cylinder is hence alternately pushed forward and backward. The volumes of the first and second sub-cylinders are changed to compress air in the first sub-cylinder or the second sub-cylinder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of mechanical devices for the pumping of fluids which are powered by a brushless linear motor with permanent magnets.

2. Description of the Related Art

The oxygen therapeutic devices include oxygen concentrator, compressing oxygen bottle, oxygen regulator, liquefied oxygen, flow regulator etc. Oxygen therapeutic devices are primarily used for chronic obstructive pulmonary disease, oxygen supply during sleep and hypoxemia. The patients can be classified into mobile and immobile. 80% patients need oxygen for 1.5 to 2.0 liter per minute and for 15 hours every day. The mobile patients may need portable and stationary oxygen devices in their daily life. When they do exercise, the demanded oxygen flow rate is increased to 4˜6 liters per minute. The oxygen concentrator extracts oxygen from air, whose key elements is therapeutic-level compressor, which requires advanced technique and innovative electro-mechanic design to meet various demands of the mobile patients.

US Publication Application No. 2006/0216170A1 provides a compressor with a cylinder of single chamber, which employs a magnetic armature and a piston as motor and electromagnetic winding sets as stator. When an AC voltage is applied to the electromagnetic winding sets, a magnetic force is intermittently induced between the electromagnetic winding sets to attract the magnetic armature to move forward so as to push the piston connected with a rear end of the magnetic armature forward. A spring disposed at a front end of the magnetic armature is compressed. When the magnetic force disappears, the spring is restored, and hence pushing the magnetic armature and piston back to the original positions. This compressor employs the magnetic force and restore of the spring as the driving force of the motor, which is smaller. Moreover, the compressor has a longer length and thus a larger size. This compressor employs the single-chamber cylinder with a fixed volume. The cross-sectional area and flow quantity of the cylinder are small. The application of this kind of compressor is limited.

U.S. Pat. No. 6,015,270 provides a compressor, which employs a movable single-chamber cylindrical piston with a plurality of magnetic flux carrying means (permanent magnet arrays) as a motor and a stationary hollow cylindrical motor body with a plurality of electromagnetic winding coils as a stator. When the plurality of drive coils sequentially excited by a multiphase current to produce force on the stator, the cylindrical piston can be moved. By changing the phase of the current applied to each coils alternately, the cylinder can be moved forward and backward. Because this compressor use the electronically controlled multiphase linear motor as the driving force, a control circuitry is required. Moreover, the design of the compressor is complex and difficult to build and has a lower power density.

SUMMARY OF THE INVENTION

The present invention provides a fluid pumping apparatus with less noise, size and weight while maintaining its operation performance to meet the demands of long-term respiratory care and quality of the patients' life.

The present invention provides a brushless linear compressor with permanent magnets mainly comprising a movable cylinder, at least one stationary electromagnetic winding set and a pair of stationary pistons. The movable cylinder has at least one permanent magnet array and a partition plate, and having one opening formed at each of two ends thereof. The partition plate is disposed in the movable cylinder to separate the movable cylinder into a first sub-cylinder and a second sub-cylinder. The permanent magnet array is disposed at an outer wall of the movable cylinder in an axial direction thereof. The magnet array includes a plurality of permanent magnets wherein adjacent magnets are magnetized oppositely. The stationary electromagnetic winding set is disposed at outside of the movable cylinder relative to the permanent magnet array. The stationary electromagnetic winding set includes a plurality of sub-winding sets. The sub-winding sets are wound in a way that the stationary electromagnetic winding set generates alternate magnetic fields to attract or repel the permanent magnet arrays to move the movable cylinder along the axial direction when an alternate current is applied. Each of the stationary pistons has a main chamber with a front end thereof placed in the opening of one of the two ends of the movable cylinder and a rear end of the main chamber becomes open. The main chamber has a plurality of sub-chambers. At least two check valves are disposed to obtain unidirectional inflow and outflow in the movable cylinder. Determining by the phase of the input current, the movable cylinder moves forward or backward along the axial direction, and accordingly compressing the volume of the first or second sub-cylinders.

The present brushless and linear design has fewer elements and better operation performance. In addition, the movable cylinder associated with the motor saves the extended length required by other moving piston designs and thus make the pumping assembly more compact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a brushless linear compressor with permanent magnets according to a first preferred embodiment of the present invention;

FIG. 2 is a perspective view of the brushless linear compressor with permanent magnets;

FIGS. 3A to 3C is perspective views of the brushless linear compressor with permanent magnets under different displacement of the movable cylinder;

FIGS. 4A to 4C is schematic cross-sectional views of the primary structure of the brushless linear compressor with permanent magnets under different displacement of the movable cylinder corresponding to FIGS. 3A to 3C, respectively;

FIG. 5A is a schematic cross-sectional view of the primary structure of a brushless linear compressor with permanent magnets according to a second preferred embodiment of the present invention;

FIG. 5B and FIG. 5C are schematic side views of variations of the primary structure of the brushless linear compressor with permanent magnets of FIG. 5A;

FIG. 6A to FIG. 6C are schematic views of variations of the stationary electromagnetic winding set of the present invention;

FIG. 7A and FIG. 7B are schematic cross-sectional views of the primary structure of a brushless linear compressor with permanent magnets according to a third preferred embodiment respectively under different displacement of the movable cylinders;

FIG. 8A is a schematic cross-sectional view of the primary structure of a brushless linear compressor with permanent magnets according to a forth preferred embodiment;

FIG. 8B is a schematic cross-sectional view of the primary structure of a brushless linear compressor with permanent magnets according to a forth preferred embodiment in the first stage of compression;

FIG. 8C is a schematic cross-sectional view of the primary structure of a brushless linear compressor with permanent magnets according to a forth preferred embodiment in the second stage of compression; and

FIG. 8D is a schematic cross-sectional view of the primary structure of a brushless linear compressor with permanent magnets according to a fifth preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The brushless linear compressor with permanent magnets of the present invention will be described in detail in accordance with the following preferred embodiments and accompanying drawings.

FIG. 1 is an exploded view of the brushless linear compressor with permanent magnets according to a first preferred embodiment of the present invention. FIG. 2 is a perspective view of the brushless linear compressor with permanent magnets of FIG. 1 after assembled. FIGS. 3A to 3C are perspective views of the brushless linear compressor with permanent magnets under different displacement of the movable cylinder. FIGS. 4A to 4C are schematic cross-sectional views of the primary structure of the brushless linear compressor with permanent magnets under different displacement of the movable cylinder corresponding to FIGS. 3A to 3C, respectively. According to the first preferred embodiment in FIG. 1, the brushless linear compressor with permanent magnets 1 mainly includes an outer shell 10, a movable cylinder 12, a pair of stationary electromagnetic winding sets 14 a and 14 b (shown in FIG. 2), a pair of stationary pistons 16 a and 16 b and a pair of chamber covers 18 a and 18 b. The outer shell 10 can be an aluminum-extruded housing for accommodating the movable cylinder 12 and the pair of stationary pistons 16 a and 16 b along the axial direction thereof. A pair of sliding rails 102 a and 102 b is disposed at two opposite positions of the top inner wall of the outer shell 10 along the axial direction thereof and a pair of sliding rails 104 a and 104 b is disposed at two opposite positions of the bottom inner wall of the outer shell 10 along the axial direction. The two pairs of sliding rails 102 and 104 are used to guide the movement of the movable cylinder 12 in the outer shell 10 along its axial direction, but the present invention is not limited to this design. For example, a pair of sliding rails can be symmetrically disposed at the middle positions of the top and bottom inner walls of the outer shell 12. Alternatively, the sliding rails 102 a and 104 b can be omitted and only using the sliding rails 104 a and 102 b, and vice versa. The present invention can also be provided with a single sliding rail disposed at the middle position of the bottom inner wall of the outer shell 10 to guide the movement of the movable cylinder 12. In the other hand, the present invention can also be provided with a sliding rail at the middle position of the top inner wall of the outer shell 10 to guide the movement of the movable cylinder 12. The movable cylinder 12 can be an aluminum-extruded cylinder with its two ends respectively formed of one opening. A partition plate 122 (shown in FIG. 2) is disposed at a position, for example a middle position, in the movable cylinder 12 to separate the movable cylinder 12 into a first sub-cylinder 120 a and a second sub-cylinder 120 b. The partition plate 122 is detachable and can have different thicknesses. A pair of permanent magnet arrays 124 a and 124 b is disposed at two opposite positions of the outer wall of the movable cylinder 12. Each of the permanent magnet arrays 124 a and 124 b has a plurality of permanent magnets wherein adjacent magnets are magnetized oppositely. The present invention preferably can provide a magnetic-conductive material 126 a or 126 b between the outer wall of the movable cylinder 12 and the permanent magnet array 124 a, or between the outer wall of the movable cylinder 12 and the permanent magnet array 124 b. The magnetic-conductive material can be silicon steel to further reduce magnetoresistance of the permanent magnet arrays 124 a and 124 b. The pair of stationary electromagnetic winding sets 14 a and 14 b are disposed at the inner wall of the outer shell 10 respectively corresponding to one of the permanent magnet arrays 124 a and 124 b (the pair of the stationary electromagnetic winding sets 14 a and 14 b are not shown in FIG. 1). According to FIG. 4A, the stationary electromagnetic winding set (14 a or 14 b) includes a stator base 140 and a winding 142. The stator base 140 has three lateral branches 140 a, 140 b and 140 c and the winding 142 is wound on the lateral branches 140 a and 140 c to form sub-winding sets. The winding way of the stationary electromagnetic winding sets 14 a or 14 b is not limited to that shown in FIG. 4, but relied on the way that makes the adjacent lateral branches of the stationary electromagnetic winding sets 14 a and 14 b generate opposite magnetic fields when a current is applied. FIGS. 6 A to 6C show other winding ways of the stationary electromagnetic winding sets. FIG. 6A shows the winding 142 is wound on the portions of the body of the stator base 140 between the lateral branches 140 a, 140 b and 140 c. FIG. 6B shows the winding 142 is wound on each of the lateral branches 140 a, 140 b and 140 c. FIG. 6C shows the winding 142 is only wound on the middle branch 140 b. These three winding ways all make the stationary electromagnetic winding sets 14 a and 14 b generate opposite magnetic fields between adjacent branches. Similarly, the number of the sub-winding sets and lateral branches of the stationary electromagnetic winding sets 14 a and 14 b is not limited to that shown in the figures, and can be modified according to the number of magnets in the permanent magnet array (124 a and 124 b) and the strength of the magnetic field demanded. As shown in FIG. 4A, the stationary piston (16 a or 16 b) has a main chamber (160 a or 160 b) with a front end thereof respectively placed in the opening of one end of the movable cylinder 12. The main chambers, 160 a and 160 b, are separated into two concentric sub-chambers 162 a and 164 a, or 162 b and 164 b, respectively. The front end of the main chamber 160 a is disposed with two check valves 166 a and 168 a with different flow directions corresponding to the sub-chambers 162 a and 164 a, respectively. The front end of the main chamber 160 b is disposed with two check valves 166 b and 168 b with different flow directions corresponding to the sub-chambers 162 b and 164 b, respectively. The check valve 166 a of the main chamber 160 a and the check valve 168 b of the main chamber 160 b have the same flow direction. The check valve 168 a of the main chamber 160 a and the check valve 166 b of the main chamber 160 b have the same flow direction. The rear ends of the main chambers 160 a and 160 b are opened and respectively covered with the chamber covers 18 a and 18 b, as shown in FIG. 2. Openings 180 a and 180 b pass through the middle portions of the chamber covers 18 a and 18 b, respectively, and communicate with the sub-chambers 162 a and 162 b. The sub-chambers 162 a and 162 b are designated to communicate with the fluid source, such as the atmosphere. A lower portion of the chamber cover 18 a is formed with a smaller opening 182 a for communicating the sub-chamber 164 a with a gas conduit of an external device, for example, a high-pressure receiving conduit of an oxygen concentrator. Similarly, an upper portion of the chamber cover 18 b is formed of a smaller opening 182 b corresponding to the sub-chamber 164 b for communicating the sub-chamber 164 b with the same gas conduit or another gas conduit of the same external device, for example, the same high-pressure receiving conduit, or a different high-pressure receiving conduit of the oxygen concentrator. The main chambers 160 a and 160 b of the stationary pistons 16 a and 16 b can be divided into one upper sub-chamber and one lower sub-chamber instead of the concentric arrangement as shown in FIG. 2.

The present invention is provided with the sliding rails at the inner wall of the outer shell 10 to guide the movement of the movable cylinder 12 along the axial direction in the outer shell 10. The present invention can also employ the stationary pistons 16 a and 16 b to guide the movement of the movable cylinder 12 along the axial direction in the outer shell 10.

The operation of the brushless linear compressor with permanent magnets 1 of the present invention will be described in detail accompanying with FIGS. 3A through FIG. 3C and FIGS. 4A through FIG. 4C as follows.

The brushless linear compressor with permanent magnets 1 of the present invention can be directly driven by the household alternate current source. The direction of the magnetic fields of the sub-winding sets of the pair of the stationary electromagnetic winding sets 14 a and 14 b is alternately changed with the phase of the alternate current source. The movable cylinder 12 is attracted or repelled to move forward or backward to alternately compress the volumes of the first sub-cylinder 120 a and the second sub-cylinder 120 b. Compressed gas, such as high pressure air, is generated in the first sub-cylinder 120 a and the second sub-cylinder 120 b, alternately. The operation of the present invention as an air compressor is described in the following. As illustrated in FIGS. 3A and 4A, when no current is applied, the lateral branches of the stationary electromagnetic winding sets 14 a and 14 b would not generate magnetic fields. The magnetic fields of the permanent magnet arrays 124 a and 124 b of the movable cylinder 12 would attract the corresponding lateral branches of the stationary electromagnetic winding sets 14 a and 14 b. The permanent magnet arrays are designed so that the movable cylinder 12 is kept at the central and balanced location. Under this circumstance, the air pressure in the first sub-cylinder 120 a and the second sub-cylinder 120 b is kept constant. As illustrated in FIGS. 3B and 4B, when the phase of the current applied to the stationary electromagnetic winding sets 14 a and 14 b is positive, the adjacent lateral branches of the stationary electromagnetic winding sets 14 a and 14 b generate alternately opposite magnetic fields to attract the corresponding magnets of the permanent magnet arrays 124 a and 124 b so as to push the movable cylinder 12 forward to one side. Therefore, the volume of the second sub-cylinder 120 b is compressed and the volume of the first sub-cylinder 120 a is expanded. Under this circumstance, compressed air is generated inside the second sub-cylinder 120 b, and flowing into the sub-chamber 164 b via the check valve 168 b. Then, the compressed air enters the high-pressure receiving conduit of the oxygen concentrator connected therewith via the opening 182 b (please refer to FIG. 1). The air pressure inside the first sub-cylinder 120 a is lowered. As a result, the atmosphere flows into the first sub-cylinder 120 a via the sub-chamber 162 a and the check valve 166 a. Moreover, the high-pressure air of the second sub-cylinder 120 b flows into the sub-chamber 164 b of the stationary piston 16 b, making the sub-chamber 164 b outwardly expanded, and the sealing between the stationary piston 16 b and the movable cylinder 12 become tighter. As illustrated in FIGS. 3C and 4C, when the phase of the current applied to the stationary electromagnetic winding sets 14 a and 14 b is negative, the magnetic fields generated on the sub-winding sets of the stationary electromagnetic winding sets 14 a and 14 b reverse to repel the movable cylinder 12 backward to the other side. Therefore, the first sub-cylinder 120 a is compressed while the second sub-cylinder 120 b is expanded. Under this circumstance, the compressed air is generated inside the first sub-cylinder 120 a, and flowing into the sub-chamber 164 a via the check valve 168 a. Then, the compressed air enters the high-pressure receiving conduit of the oxygen concentrator connected therewith (please refer to FIG. 1) via the opening 182 a. The air pressure inside the second sub-cylinder 120 b is lowered such that the atmosphere flows into the second sub-cylinder 120 b via the opening 180 b (please refer to FIG. 1), the sub-chamber 162 b and the check valve 166 b. The sub-chamber 164 a is outwardly expanded due to higher pressure, and thus the sealing between the stationary piston 16 a and movable cylinder 12 become tighter.

The partition plate 122 inside the movable cylinder 12 is detachable. The air compression ratio inside the movable cylinder 12 is adjustable by the replacement of the partition plate 122 of different thicknesses. The air compression ratio is defined as the ratio of the maximum expanded volume to the minimum compressed volume of the first sub-cylinder 120 a or the second sub-cylinder 120 b. The pressure and flow quantity of the compressed air are thereby adjustable. Moreover, the present invention can be incorporated with a Pulse-Width-Module frequency controller and a sensing circuit to precisely control the high air pressure and its flow rate.

FIG. 5A is a schematic cross-sectional view of a brushless linear compressor with permanent magnets according to a second preferred embodiment of the present invention. The difference between the second and first preferred embodiments is that the outer wall of the movable cylinder 12 is provided with only one permanent-magnet array 124 along its axial direction, and a stationary electromagnetic winding set 14 is correspondingly disposed at the inner wall of the outer shell 10. The remaining constitution elements of the second preferred embodiment are the same with that of the first preferred embodiment. Besides, the number of the permanent magnet arrays disposed at the outer wall of the movable cylinder 12 along its axial direction is not limited to the above-described embodiments. The outer wall of the movable cylinder 12 along its axial direction can be provided with the permanent magnet arrays arranged in a geometric relationship such triangular shape (FIG. 5B), cross shape or X shape (FIG. 5C). The number of the stationary electromagnetic winding sets is determined by the number of the permanent magnet arrays.

FIGS. 7A and 7B show schematic cross-sectional views of the primary structure of a brushless linear compressor with permanent magnets under different displacement of the movable cylinders according to a third preferred embodiment of the present invention. In the third embodiment, the present invention employs the double-motor-four-subcylinder design. More specifically, the third preferred embodiment is composed of two movable cylinders with brushless linear motors connected together via a common-used stationary piston disposed therebetween. The brushless linear compressor with permanent magnets of the third preferred embodiment mainly include a first movable cylinder 72, a second movable cylinder 76, a pair of first stationary electromagnetic winding sets 74 a and 74 b, a pair of second stationary electromagnetic winding sets 78 a and 78 b, a first stationary piston 80, a second stationary piston 82 and a third stationary piston 84. A pair of permanent magnet arrays 724 a and 724 b is disposed at an outer wall of the first cylinder 72 along its axial direction. Each of the permanent magnet arrays 724 a and 724 b includes a plurality of permanent magnets wherein adjacent magnets are magnetized oppositely. A magnetic-conductive material 726 a, for example silicon steel, is preferably disposed between the outer wall of the first movable cylinder 72 and the corresponding permanent magnet array 724 a to reduce magnetoresistance of the permanent magnet array 724 a. A magnetic-conductive material 726 b, for example silicon steel, is preferably disposed between the outer wall of the first movable cylinder 72 and the corresponding permanent magnet array 724 b to reduce magnetoresistance of the permanent magnet array 724 b. A detachable first partition plate 722 is disposed inside the first movable cylinder 72 to separate the first movable cylinder 72 into a first sub-cylinder 72 a and a second sub-cylinder 72 b. The pair of the first stationary electromagnetic winding sets 74 a and 74 b are disposed outside of the first movable cylinder 72 corresponding to the permanent magnet arrays 724 a and 724 b, respectively. The design of the first stationary electromagnetic winding sets 74 a and 74 b is the same with the design of the stationary electromagnetic winding sets 14 a and 14 b of the first preferred embodiment. Each of the first stationary electromagnetic winding sets (74 a or 74 b) includes a stator base 740 and windings 742. Each winding wound on a lateral branch of the stator base 740 forms a sub-winding set. The first stationary electromagnetic winding sets 74 a and 74 b generate alternate magnetic fields when the current is applied. The first stationary piston 80 includes a first main chamber divided into two first sub-chambers 802 and 804. The front end of the first stationary piston 80 is placed in the opening of one end of the movable cylinder 72. Two check valves 806 and 808 with different flow directions are disposed at the front end of the first movable cylinder 72 corresponding to the first sub-chambers 802 and 804, respectively.

A pair of permanent magnet arrays 764 a and 764 b is disposed at the outer wall of the second cylinder 76. Each of the permanent magnet arrays 764 a and 764 b includes a plurality of permanent magnets wherein adjacent magnets are magnetized oppositely. A magnetic-conductive material 766 a, for example silicon steel, is preferably disposed between the outer wall of the second movable cylinder 76 and the corresponding permanent magnet array 764 a to reduce the magnetoresistance of the permanent magnet array 764 a. Similarly, a magnetic-conductive material 766 b, for example silicon steel, is preferably disposed between the outer wall of the second movable cylinder 76 and the corresponding permanent magnet array 764 b to reduce the magnetoresistance of the permanent magnet array 764 b. A detachable second partition plate 762 is disposed at a location, for example a central location, inside the second movable cylinder 76 to separate the second movable cylinder 76 into a third sub-cylinder 76 a and a fourth sub-cylinder 76 b. The pair of the second stationary electromagnetic winding sets 78 a and 78 b is disposed outside of the second movable cylinder 76 corresponding to one of the permanent magnet arrays 764 a and 764 b, respectively. The design of the second stationary electromagnetic winding sets 78 a and 78 b is the same with the design of the stationary electromagnetic winding sets 14 a and 14 b of the first preferred embodiment. Each of the second stationary electromagnetic winding sets (78 a or 78 b) includes a stator base 780 and windings 782. Each winding wound on a lateral branch of the stator base 780 forms a sub-winding set. The second stationary electromagnetic winding sets 78 a and 78 b generate alternate magnetic fields when the current is applied. The second stationary piston 82 includes a second main chamber divided into two sub-chambers 822 and 824. A front end of the second stationary piston 82 is placed in the opening of one end of the second movable cylinder 76. Two check valves 826 and 828 with different flow directions are disposed at the front end of the second movable cylinder 76 corresponding to the second sub-chambers 822 and 824, respectively.

The third stationary piston 84 includes a third main chamber divided into two third sub-chambers 843 and 844. A front end 841 of the third stationary piston 84 is placed into the opening of the other end of the first movable cylinder 72. A rear end 842 of the third stationary piston 84 is placed in the opening of the other end of the second movable cylinder 76. As such, the first movable cylinder 72 and the second movable cylinder 76 are connected together via the third stationary piston 84. Two check valves 845 and 846 with different flow directions are disposed at the front end 841 of the third stationary piston 84 corresponding to the third sub-chambers 843 and 844, respectively. Two check valves 847 and 848 with different flow directions are disposed at the rear end 842 of the third stationary piston 84 corresponding to the third sub-chambers 843 and 844, respectively. An upper part of the third sub-chamber 843 is formed with an outlet passage 849 and a lower part of the third sub-chamber 844 is formed with an inlet passage 850.

In the third preferred embodiment, it is preferable that the arrangement of the magnetic fields generated by the pair of the first stationary electromagnetic winding sets 74 a and 74 b is opposite to the arrangement of the magnetic fields generated by the pair of the second stationary electromagnetic winding sets 78 a and 78 b. That is, the winding direction and the current direction of the first stationary electromagnetic winding sets 74 a and 74 b are opposite to the second stationary electromagnetic winding sets 78 b and 78 b. As shown in FIG. 7A, when the phase of the alternate current is positive, the sequence of magnetic fields at the lateral branches of the first stationary electromagnetic winding sets 74 a and 74 b is N-S-N, while the sequence of the magnetic fields at the lateral branches of the second stationary electromagnetic winding sets 78 a and 78 b is S-N-S. Under this circumstance, the first movable cylinder 72 moves toward the front end 841 of the third stationary piston 84 to expand the volume of the first sub-cylinder 72 a while compressing the volume of the second cylinder 72 b. Compressed air generated inside the second sub-cylinder 72 b flows into the third sub-chamber 843 of the third stationary piston 84 via the check valve 845, while the atmosphere enters the first sub-cylinder 72 a via the first sub-chamber 804 of the first stationary piston 80. At the same time, the second movable cylinder 76 moves toward the rear end 842 of the third stationary piston 84 to compress the volume of the third sub-cylinder 76 a, while expanding the volume of the fourth sub-cylinder 76 b. Compressed air is generated inside the third sub-cylinder 76 a, and flowing into the third sub-chamber 843 of the third stationary piston 84 via the check valve 847. The atmosphere enters the second sub-cylinder 76 b via the second sub-chamber 824 of the second stationary piston 82. The compressed air from the first movable cylinder 72 and the second movable cylinder 76 at the same time enters the third sub-chamber 843 of the third stationary piston 84, and then flowing into a high-pressure receiving conduit of the external device, for example, an oxygen concentrator connected therewith via the outlet passage 849.

As show in FIG. 7B, when the phase of the applied alternate current is negative, the sequence of the magnetic fields generated by the first stationary electromagnetic winding sets 74 a and 74 b is S-N-S. While the arrangement of the magnetic fields generated by the second stationary electromagnetic winding sets 76 a and 76 b is N-S-N. Under this circumstance, the first movable cylinder 72 moves away from the front end 841 of the third stationary piston 84 to compress the volume of the first sub-cylinder 72 a, while expanding the volume of the second sub-cylinder 72 b. The compressed air generated inside the first sub-cylinder 72 a flows into first sub-chamber 802 of the first stationary piston 80 via the check valve 806, and then entering a high-pressure receiving passage of an external device connected therewith. As to the second movable cylinder 76 which moves away from the rear end 842 of the third stationary piston 84 at the same time to expand the volume of the third sub-cylinder 76 a, and to compress the volume of fourth sub-cylinder 76 b. The compressed air inside the fourth sub-cylinder 76 b flows into the second sub-chamber 822 of the second stationary piston 82 via the check valve 826, and then entering a high-pressure receiving conduit of an external device connected therewith. The atmospheric air flows into the third sub-chamber 844 via the inlet gas passage 850 of the third stationary piston 84, and then entering the second sub-cylinder 72 b of the first movable cylinder 72 and the third sub-cylinder 76 a of the second movable cylinder 76.

In the third preferred embodiment, when the current is applied to the first and the second brushless linear motors, the compressed air generated by the first movable cylinder 72 and the second movable cylinder 76 enters the outlet passage 849 at the same time. The flow rate of the compressed air is doubled. Moreover, the first movable cylinder 72 and the second movable cylinder 76 move relative to each other at the same time. The vibration generated by both brushless linear motors is canceled by each other. The noise is reduced as well.

The remaining constitution elements of the brushless linear compressor with permanent magnets of the third preferred embodiment are the same with that of the first preferred embodiment as shown in FIG. 1. The number of the permanent magnet arrays disposed at the outer walls of the first movable cylinder 72 and the second movable cylinder 76 and their arrangements can also have various alternatives as described in the above preferred embodiments. The outer shell, movable cylinder, stationary piston and the chamber cover of the present brushless linear compressor with permanent magnets can be made by the low-cost aluminum-extrusion and plastic injection. The assembling process is simplified and the fabrication cost is lowered.

FIG. 8A is a schematic cross-sectional view of a two stage brushless linear compressor with permanent magnets according to a forth preferred embodiment of the present invention. The difference between the forth and first preferred embodiments is that at least one interstage check valve 167 is disposed in the partition plate 122. The first stationary piston 16 a is preferred to have a single main chamber 160 a and at least one intake check valve 166 a. The second stationary piston 16 b is preferred to have a single main chamber 160 b and at least one discharge check valve 168 b. The first sub-cylinder 120 a performs the first stage of compression while the second sub-cylinder 120 b performs the second stage of compression. The first stage of compression is illustrated in FIG. 8B. As the movable cylinder 12 moves toward the first stationary piston 160 a, the fluid in the first sub-cylinder 120 a is compressed and enters the second sub-cylinder 120 b via the interstage check valve 167. The second stage of compression is illustrated in FIG. 8C. As the movable cylinder 12 moves toward the second stationary piston 160 b, the fluid in the second sub-cylinder 120 b is compressed and enters the second main chamber 160 b of the second stationary piston 160 b via the discharge check valve 168 b. Meanwhile, the fluid from the first main chamber 160 a of the first stationary piston 16 a enters the first sub-cylinder 120 a via the intake check 166 a.

FIG. 8D is a schematic cross-sectional view of a two stage brushless linear compressor with permanent magnets according to a fifth preferred embodiment of the present invention. The difference between the fifth and forth preferred embodiments is that the outer diameter of the second stationary piston 16 b and the inner diameter of the second sub-cylinder 120 b are smaller than the outer diameter of the first stationary piston 16 a and the inner diameter of the first sub-cylinder 120 a, respectively. This arrangement can provide higher pressure output in the second stage of compression with the same linear motor force.

The remaining constitution elements of the forth and fifth preferred embodiments are the same with that of the first preferred embodiment. The alternations and modifications of the sliding rails and the permanent magnet arrays as described in the above preferred embodiments are also applicable in the forth and fifth preferred embodiments.

While the invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A linear compressor with permanent magnets comprising: a movable cylinder having at least one permanent magnet array and a partition plate, said movable cylinder having one opening formed at each of two ends thereof, said partition plate disposed in said movable cylinder to separate said movable cylinder into a first sub-cylinder and a second sub-cylinder, said permanent magnet array disposed at an outer wall of said movable cylinder in an axial direction thereof and including a plurality of permanent magnets in which adjacent magnets are magnetized oppositely; at least one stationary electromagnetic winding set disposed at outside of said movable cylinder relative to said permanent magnet array, said stationary electromagnetic winding set including a plurality of lateral branches and a plurality of sub-winding sets, wherein said sub-winding sets are wound in a way that said stationary electromagnetic winding set generates alternate magnetic fields to attract or repel said movable cylinder to move along the axial direction when an alternate current is applied to said stationary electromagnetic winding set; and a pair of stationary pistons, each of said stationary pistons having a main chamber with a front end thereof placed in the opening of one said end of said movable cylinder and a rear end of said main chamber becoming open, said main chamber having a plurality of sub-chambers and at least two check valves with different flow directions disposed at said front end thereof respectively corresponding to one of said sub-chambers; wherein said movable cylinder moves forward or backward along the axial direction in response to a phase of the current applied to said stationary electromagnetic winding set, and accordingly changing volumes of said first sub-cylinder and said second sub-cylinder.
 2. The compressor of claim 1, further comprising an outer shell for accommodating said movable cylinder, said stationary electromagnetic winding set and the pair of said stationary pistons, wherein said movable cylinder and the pair of said stationary pistons are disposed in a way along an axial direction of said outer shell, and said stationary electromagnetic winding set is disposed at an inner sidewall of said outer shell.
 3. The compressor of claim 2, further comprising at least a pair of sliding rails respectively disposed at two opposite positions of one inner wall of said outer shell along the axial direction thereof for guiding the movement of said movable cylinder.
 4. The compressor of claim 1, wherein the pair of said stationary pistons guides the movement of said movable cylinder.
 5. The compressor of claim 1, wherein said movable cylinder has a plurality of said permanent magnet arrays symmetrically disposed at the outer wall of said movable cylinder, and a plurality of said stationary electromagnetic winding sets are disposed at outside of said movable cylinder respectively corresponding to one of said permanent magnet arrays.
 6. The compressor of claim 5, wherein said permanent magnet arrays are disposed at the outer wall of said movable cylinder in a geometric arrangement of cross shape, X shape or triangular shape.
 7. The compressor of claim 2, wherein said movable cylinder has a plurality of said permanent magnet arrays symmetrically disposed at the outer wall of said movable cylinder, and a plurality of said stationary electromagnetic winding sets is disposed at the inner wall of said outer shell respectively corresponding to one of said permanent magnet arrays.
 8. The compressor of claim 7, wherein said permanent magnet arrays are disposed at the outer wall of said movable cylinder in a geometric arrangement of cross shape, X shape or triangular shape.
 9. The compressor of claim 1, wherein said partition plate is detachable.
 10. The compressor of claim 1, further comprising a magnetic-conductive material disposed between said permanent magnet arrays and the outer wall of said movable cylinder.
 11. A linear compressor with permanent magnets, comprising: a first movable cylinder having at least one first permanent magnet arrays and a first partition plate, said first movable cylinder having one opening respectively formed at each of two ends thereof, said partition plate disposed in said first movable cylinder to separate said first movable cylinder into a first sub-cylinder and a second sub-cylinder, said first permanent magnet array disposed at an outer wall of said first movable cylinder in an axial direction thereof and having a plurality of permanent magnets in which adjacent magnets are magnetized oppositely; a second movable cylinder having at least one second permanent magnet arrays and a second partition plate, said second movable cylinder having one opening respectively formed at each of two ends thereof, said second partition plate disposed in said second movable cylinder to separate said second movable cylinder to a third sub-cylinder and a fourth sub-cylinder, said second permanent magnet arrays disposed at an outer wall of said second movable cylinder along an axial direction thereof and having a plurality of permanent magnets in which adjacent magnets are magnetized oppositely; at least a first stationary electromagnetic winding set disposed outside said first movable cylinder relative to said first permanent magnet array, said first stationary electromagnetic winding set including a plurality of lateral branches and a plurality of sub-winding sets, wherein said sub-winding sets are wound in a way that said first stationary electromagnetic winding set generates alternative positive and negative magnetic fields to attract or repel said first movable cylinder to move along the axial direction when an alternate current is applied to said first stationary electromagnetic winding set; at least a second stationary electromagnetic winding set disposed outside said second movable cylinder relative to said permanent magnet array, said second stationary electromagnetic winding set including a plurality of lateral branches and a plurality of sub-winding sets, wherein said sub-winding sets are wound in a way that said second stationary electromagnetic winding set generates alternate positive and negative magnetic fields to attract or repel said second movable cylinder to move along the axial direction when a alternate current is applied into said second stationary electromagnetic winding set; a first stationary piston having a first main chamber with a front end thereof placed in the opening of one said end of said first movable cylinder and a rear end thereof becoming open, said first main chamber including a plurality of first sub-chambers with a front end thereof provided with at least two check valves having different flow directions respectively corresponding to one of said first sub-chambers; a second stationary piston having a second main chamber with a front end thereof placed in the opening of one said end of said second movable cylinder and a rear end thereof becoming open, said second main chamber including a plurality of second sub-chambers with a front end thereof provided with at least two check valves having different flow directions respectively corresponding to one of said second sub-chambers; and a third stationary piston having a third main chamber, said third main chamber having two third sub-chambers, an outlet passage and an inlet passage, a front end of said third main chamber placed in the opening of the other end of said first movable cylinder and a rear end thereof placed in the opening of the other end of said second movable cylinder, the front and rear ends of said third main chamber respectively provided with two check valves with different flow directions corresponding to said third sub-chambers, said outlet passage formed at one side of one of said third sub-chambers, and said inlet passage formed at one side of the other one of said third sub-chambers; wherein said first movable cylinder and said second movable cylinder move forward or backward along the axial direction in response to a phase of the current applied to said first stationary electromagnetic winding set and said second stationary electromagnetic winding set.
 12. The compressor of claim 11, further comprising an outer shell for accommodating said first movable cylinder, said second movable cylinder, said first stationary electromagnetic winding set, said second stationary electromagnetic winding set, said first stationary piston, said second stationary piston and said third stationary piston, wherein said first and second movable cylinders and said first, second and third stationary pistons are disposed along an axial direction of said outer shell, said first and second stationary electromagnetic winding sets are disposed at an inner wall of said outer shell.
 13. The compressor of claim 12, further comprising at least a pair of sliding rails disposed at two opposite positions of the inner wall of said outer shell along the axial direction thereof for guiding the movement of said first and second movable cylinders.
 14. The compressor of claim 11, wherein said first, second and third stationary pistons guide the movement of said first, second and third movable cylinders.
 15. The compressor of claim 11, wherein a plurality of first permanent magnet arrays and a plurality of second permanent magnet arrays respectively and symmetrically disposed at an outer wall of said first movable cylinder and said second movable cylinder, and a plurality of said first stationary electromagnetic winding sets and a plurality of said second stationary electromagnetic winding sets are respectively disposed outside said first movable cylinder and said second movable cylinder corresponding to said first permanent magnet arrays and said second permanent magnet arrays.
 16. The compressor of claim 15, wherein said first permanent magnet arrays and said second permanent magnet arrays are respectively disposed at the outer walls of said first movable cylinder and said second movable cylinder in a geometric arrangement of cross shape, X shape or triangular shape.
 17. The compressor of claim 11, wherein said first partition plate and said second partition plate are detachable.
 18. The compressor of claim 11, further comprising a first magnetic-conductive material disposed between said first permanent magnet array and the outer wall of said first movable cylinder and a second magnetic-conductive material disposed between said second permanent magnet array and the outer wall of said second movable cylinder.
 19. A two stage linear compressor with permanent magnets comprising: a movable cylinder having at least one permanent magnet array and a partition plate, said movable cylinder having one opening formed at each of two ends thereof, said partition plate having at least one interstage check valve and disposed in said movable cylinder to separate said movable cylinder into a first sub-cylinder and a second sub-cylinder, said permanent magnet array disposed at an outer wall of said movable cylinder in an axial direction thereof and including a plurality of permanent magnets in which adjacent magnets are magnetized oppositely; at least one stationary electromagnetic winding set disposed at outside of said movable cylinder relative to said permanent magnet array, said stationary electromagnetic winding set including a plurality of lateral branches and a plurality of sub-winding sets, wherein said sub-winding sets are wound in a way that said stationary electromagnetic winding set generates alternate magnetic fields to attract or repel said movable cylinder to move along the axial direction when an alternate current is applied to said stationary electromagnetic winding set; a first stationary pistons, said first stationary pistons having a main chamber with a front end thereof placed in the opening of said first sub-cylinder and a rear end of said main chamber becoming open, said main chamber having at least one intake check valve disposed at said front end thereof; and a second stationary pistons, said second stationary pistons having a main chamber with a front end thereof placed in the opening of said second sub-cylinder and a rear end of said main chamber becoming open, said main chamber having at least one discharge check valve disposed at said front end thereof; wherein said movable cylinder moves forward or backward along the axial direction in response to a phase of the current applied to said stationary electromagnetic winding set, and accordingly changing volumes of said first sub-cylinder and said second sub-cylinder, a working fluid is drawn into said first sub-cylinder through said intake valve and is compressed and transferred through said interstage valve into the said second sub-cylinder piston in a first stage of compression, and further is compressed and transferred out of said second sub-cylinder through said discharge valve, in a second stage of compression.
 20. The compressor of claim 19, further comprising an outer shell for accommodating said movable cylinder, said stationary electromagnetic winding set and the said first and second stationary pistons, wherein said movable cylinder and the said stationary pistons are disposed in a way along an axial direction of said outer shell, and said stationary electromagnetic winding set is disposed at an inner sidewall of said outer shell.
 21. The compressor of claim 20, further comprising at least a pair of sliding rails respectively disposed at two opposite positions of one inner wall of said outer shell along the axial direction thereof for guiding the movement of said movable cylinder.
 22. The compressor of claim 19, wherein the said first and second stationary pistons guides the movement of said movable cylinder.
 23. The compressor of claim 19, wherein said movable cylinder has a plurality of said permanent magnet arrays symmetrically disposed at the outer wall of said movable cylinder, and a plurality of said stationary electromagnetic winding sets are disposed at outside of said movable cylinder respectively corresponding to one of said permanent magnet arrays.
 24. The compressor of claim 23, wherein said permanent magnet arrays are disposed at the outer wall of said movable cylinder in a geometric arrangement of cross shape, X shape or triangular shape.
 25. The compressor of claim 19, further comprising a magnetic-conductive material disposed between said permanent magnet arrays and the outer wall of said movable cylinder.
 26. The compressor of claim 19, wherein an outer diameter of said second stationary piston and an inner diameter of said second sub-cylinder are smaller than that of said first stationary piston and said first sub-cylinder, respectively. 